1. Technical Field
The present invention relates to a cleaning blade, and an image forming apparatus and a process cartridge using the cleaning blade.
2. Description of the Related Art
An electrophotographic image forming apparatus typically forms an image by the following process. Namely, first, an image bearer such as a photoconductor uniformly charged by a charger is scanned with light to form an electrostatic latent image thereon, and the electrostatic latent image is developed by an image developer. Next, a toner image formed on the image bearer by the development is directly or through an intermediate transferer on a recording sheet. An untransferred toner adhering to the surface of the image bearer is removed by a cleaning blade.
A cleaning blade using a strip-shaped elastic body is well known because of having simple constitution and good cleanability. The elastic blade is formed of an elastic body such as polyurethane rubbers. A base end of the elastic blade is fixed on a rigid holder and a tip ridgeline thereof is pressed against a circumferential surface of an image bearer such as photoreceptors to dam and scrape off a toner remaining on the image bearer.
However, when a spherical toner is used to produce high-quality images, it enters a slight gap between the cleaning blade formed of only a conventional rubber and the photoreceptor drum, and soon scrapes off from the gap, occasionally resulting in poor cleaning.
A contact pressure between the image bearer and the cleaning blade needs increasing to prevent the toner from scraping from the gap. However, when the contact pressure is increased, a friction between an image bearer 3 and a cleaning blade 62 in FIG. 5A increases, the cleaning blade 62 is drawn in a travel direction of the image bearer, and a tip ridgeline 62c of the cleaning blade 62 turns over. The cleaning blade 62 turned over occasionally makes noises when restored to its original state, resisting turning over. Further, when the cleaning continues while the tip ridgeline 62c of the cleaning blade 62 is turned over, a local abrasion is made a few μm from the tip ridgeline 62c of an edge surface 62a of the cleaning blade 62 as shown in FIG. 5B. When the cleaning continues further, the local abrasion becomes large and finally the tip ridgeline 62c is chipped as shown in FIG. 5C. When the tip ridgeline 62c lacks, a toner cannot normally be removed, resulting in poor cleaning.
In order to prevent the tip ridgeline 62c of the cleaning blade contacting the surface of the photoconductor drum from turning over, trials of hardening the edge to be difficult to deform are made. For example, a surface layer including an UV curing resin is formed on the tip ridgeline 62c of the cleaning blade or the elastic member such that the tip ridgeline 62c is hardened to prevent the tip ridgeline 62c from turning over.
Japanese published unexamined application No. JP-2010-152295-A discloses a cleaning blade which is an elastic blade formed of a urethane rubber or the like and a surface layer harder than the elastic blade, which covers a tip ridgeline part thereof contacting an image bearer. This claims the blade removes a downsized and spheroidized polymerization toner well, and prevents the blade from turning over the tip ridgeline, making a noise and being abraded to have stable cleanability for long periods.
However, the cleaning blade disclosed in Japanese published unexamined application No. JP-2010-152295-A has lower followability to fine oscillation of the image bearer to cause poor cleaning due to its tip ridgeline having high hardness. Recently, needs for image forming apparatus with electrophotographic process at higher speed have been increasing. The higher image forming speed, not less than a linear speed of 60 mm/sec, causes an axis of the image bearer rotating at high speed to finely oscillate. Therefore, the cleaning blade disclosed in Japanese published unexamined application No. JP-2010-152295-A is not sufficiently suitable for the higher speed image forming apparatus.
When the blade is hardened against turn over and abrasion, the blade deteriorates in followability. When softened to increase followability, the blade tends to turn over and easily abrade. This is a trade-off relation, and a cleaning blade preventing turn over and abrasion and having followability is required, particularly in a high-speed image forming apparatus rotating a photoreceptor drum at a high speed.